Heads issue
I agree with Pagilma. Those arent domed pistons. They are flat tops and dont look like they even stick out of the bore. My 340 has Ross flat tops tha are + .020" deck height. The heads needed to be milled to get the compression to 11:1. I bet you are closer to 9.5 or 10:1.
Here is a pictures of my exhaust ports. They flow around 170 @.550"
I agree with Pagilma. Those arent domed pistons. They are flat tops and dont look like they even stick out of the bore. My 340 has Ross flat tops tha are + .020" deck height. The heads needed to be milled to get the compression to 11:1. I bet you are closer to 9.5 or 10:1.
Here is a pictures of my exhaust ports. They flow around 170 @.550"